Mount Prospect, Illinois 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

439
FXUS63 KLOT 111156
AFDLOT

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
556 AM CST Sun Jan 11 2026

.KEY MESSAGES...

- Lingering wind-whipped snow showers and flurries ending this
  morning, followed by easing winds this afternoon.

- Up and then down temperatures are expected this week with
  occasional opportunities for precipitation.

- The main concern from a winter weather perspective is
  Wednesday into Thursday, with wind-whipped snow showers during
  the day Wednesday possibly followed by accumulating lake
  effect snow Wednesday night into Thursday morning.

&&

.DISCUSSION...
Issued at 251 AM CST Sun Jan 11 2026

Through Monday:

Scattered snow showers and flurries will gradually taper off
across the area this morning, as a deep mid-level trough and
vort max shift off to the east/southeast of the area. Can`t rule
out some light accumulations (less than half an inch) especially
southeast of the I-55 corridor early this morning as the vort
and mid-level cold pool pass overhead, though most areas will
see little/no additional accumulation. The exception to this
will be parts of north/northeast Porter county where around an
inch of accumulation is possible during a period of lake-effect
snow showers which will linger through mid-late morning.
Otherwise, blustery and colder conditions can be expected, with
decreasing cloud cover into this afternoon.

Early morning GOES water vapor imagery depicts the deep mid-
level trough and embedded closed lower over the western Great
Lakes region. An aforementioned strong vort/short wave was
rounding the base of this trough over northern IL as of 08Z/2AM,
with a cold pocket of -15C air analyzed at 850 mb. Beneath this
cold pocket, RAP soundings indicate a deeply-mixed boundary
layer with steep low-level lapse rates extending to nearly 800
mb. Resulting stratocu deck appears to be entirely within the
DGZ (-12C to -18C), producing widespread snow showers and
flurries across the area. While brief accumulations are likely
with these, their scattered convective nature and relatively
brief duration at any one location should limit amounts to less
than a half inch in most areas. The vort and associated cold-
pool will move off to the east-southeast early this morning
however, allowing snow showers to taper to scattered non-
accumulating flurries before ending. Over parts of northwest IN
(particularly Porter county), north-northwest boundary layer
flow will support lake-effect snow showers through late morning,
before strong subsidence in the wake of the upper trough
substantially lowers inversion heights. Dry air immediately
above the inversion should help to limit lake-effect snow shower
intensity somewhat even prior to that, though accumulations
around an inch appear likely.

BLustery west-northwest winds gusting 25-30 mph this morning
will gradually ease this afternoon, as weak surface high
pressure ridging develops eastward across the Mississippi
Valley. Associated subsidence should also help to decrease cloud
cover from west to east as well. With some afternoon sun,
temperatures should creep back to the lower 30s, though wind
chills will remain in the low to mid 20s.

Surface winds will then turn southwest early this evening, in
response to a quick-moving clipper dropping southeast across the
upper Mississippi Valley and into the Great Lakes region.
This will induce a 40-45 kt southwesterly low level jet
overnight, which will make for breezy surface winds and even
some sporadic gusts in the 20 mph range at times overnight.
We`ll probably see temps drop off into the mid-upper 20s during
the evening, then remain fairly steady overnight with the winds
and associated warm advection. These southwest winds will ease
on Monday as the short wave tracks off to the northeast of the
area, though continuing modest warm advection and partly cloudy
sky cover looks to support daytime highs in the lower 40s for
most areas.

Ratzer


Monday Night through Saturday:

As has been advertised, anomalously strong mid-upper ridging
will establish near the Pacific Coast through next week, with
downstream troughing carved out across much of eastern North
America. This represents the positive phase of the Pacific North
American (PNA) teleconnection pattern, typified by a predominantly
northwesterly flow pattern into the Great Lakes region.
A stretch of solidly above normal temps to start the workweek
will peak on Tuesday, followed by a return to more seasonable
readings for mid-January through the rest of the week (near to
below normal temperatures). The deep northwest flow pattern
will be unfavorable for any moisture-laden synoptic systems, so
overall precip amounts for the week will be light. This
certainly does not preclude any impactful winter weather,
however, with a persistent signal for accumulating lake snow
somewhere downwind of southern Lake Michigan Wednesday PM into
Thursday.

Forecast low temperatures Monday night are near to above normal
highs for this time of year in the lower to mid 30s. This will
provide a mild starting point for highs in the upper 40s to
around 50F on Tuesday. The next clipper-type wave tracking into
the northern Great Lakes will induce breezy west-southwest winds
gusting to 25-30 mph. Some spotty showers or sprinkles will be
possible (20-30% PoPs) from the mid-level overcast out ahead of
the system cold front, which will sweep across the area by
Tuesday evening.

Most of Tuesday night will be quiet and breezy with temperatures
still above normal. This will abruptly change by Wednesday
morning as a robust PV anomaly dives southward across the area
in tandem with a secondary cold front passage packing much
stronger cold air advection. As winds shift to north-
northwesterly with gusts up to 30-40 mph, strong large scale
forcing will result in quickly blossoming snow showers.

There`s some uncertainty in the westward extent of sufficient
moisture through the DGZ, though with good run to run continuity
in most of the ensemble systems for this period, felt
comfortable with PoPs increasing to 30-70%, highest in northeast
Illinois and northwest Indiana. Depending on how this setup
evolves from a convergence perspective, very steep low-level
lapse rates could yield embedded snow squalls. While surface
temperatures and mild antecedent ground conditions to start the
day may initially limit accumulation/impact potential,
temperatures falling into the 20s in the afternoon could paint a
different story heading into the evening commute.

The main change noted from previous model cycles is slower and
stronger with the PV anomaly/very cold closed 500 mb low diving
south across the region. This entails cyclonic flow lingering
into Wednesday night, important to most effectively tap into
good lake induced thermodynamics (vs. a more subsident regime
serving as a limiting factor). It`s much too early to be
confident in the details in this period. However from a pattern
recognition perspective, accumulating lake effect snow is
appearing more likely downwind of southern Lake Michigan,
possibly well downwind at that, due to deep near unidirectional
northerly flow and the synoptic assist from the departing PV
anomaly. Could see some hybrid aspects as with the November 9-10
event per some recent guidance member depictions. With forecast
northerly boundary layer flow, increased PoPs to 50-60%
near/east of I-57 in Illinois into northwest Indiana.

Any break following the possible lake effect snow showers may
be short-lived, with signs pointing toward an additional clipper
system or two affecting the region sometime in the Thursday
night-Saturday timeframe. Some guidance members suggest the
clipper short-wave could temporarily become a cut- off low into
the start of the weekend, which greatly increases uncertainty in
how it will evolve. Maintained broad-brushed chance PoPs
peaking in the 30-50% range Thursday night-Friday night given
approximately that much ensemble member support. Nonetheless,
the spectrum of plausible outcomes here is quite large, from on
and off light snow/snow showers to little or no snow. Expect
generally below normal temperatures to close out the week and
into next weekend.

Castro

&&

.AVIATION /12Z TAFS THROUGH 18Z MONDAY/...
Issued at 556 AM CST Sun Jan 11 2026

Main Items of Note:

- Uncertain trends with sub 3kft CIGs into this evening

- Gusty winds, from west-northwest through early afternoon, and
  then from southwest/west-southwest this evening-Monday AM

There are no significant concerns this period. Scattered
flurries are expected to end by about 15z. CIGs generally in the
2-3kft range have the potential to hang on a bit longer than
indicated in the TAFs. Blustery northwest winds will ease and
back to westerly later today. Forecast soundings suggest
prevailing gusts should return later this evening and continue
into Monday morning as winds further back to 230-240 deg. A
fairly stout low-level jet will shift overhead tonight, though
LLWS criteria appears unlikely to be met.

Castro

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...None.
IN...None.
LM...Small Craft Advisory until 3 PM CST this afternoon for
     Winthrop Harbor IL to Gary IN.

     Gale Warning until noon CST today for Gary to Burns Harbor IN-
     Burns Harbor to Michigan City IN.

     Small Craft Advisory from noon today to midnight CST tonight
     for Gary to Burns Harbor IN-Burns Harbor to Michigan City
     IN.

&&

$$

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